The present invention relates generally to the field of tire/retread manufacture, and, more particularly, to improved tires/retreads which include Trinidad Lake Asphalt as a component or raw material therein to enhance the performance and/or other characteristics of the tires/retreads.
Trinidad Lake Asphalt (hereafter "TLA"), also known as Trinidad Natural Asphalt or Epure, is a naturally occurring Lake Asphalt which is found in the island of Trinidad in the West Indies. This natural phenomenon, TLA, is different from and is not to be confused with tar sands, or tar pits or even asphalt which is a natural or mechanical mixture in which bitumen is associated with mineral matter. An accepted definition which has been given to TLA is: an asphalt which, as found in nature, is in a condition of flow or fluidity.
As dug from the earth, TLA contains thirty percent (30%) water which is normally removed through refining under conditions of temperature. The molten material is then filtered and typically packed into silicone treated hardboard drums. The drums are typically silicone treated as the temperature at which the molten TLA is filled into the drum is generally around 163.degree. C. TLA has been advantageously used in the past in paving or road building materials and applications. TLA is non-carcinogenic, is an entirely natural material, and is environmentally friendly.
In the manufacture of tires/retreads for use, for example, in connection with ground or air vehicles or the like, different compounding formulations are used. These formulations include a variety of ingredients or raw materials. For example, Asphaltenes may be used as a raw material. Process oils may also be used as a raw material. Carbon black may also be used as a raw material and is often used for reinforcing and/or networking purposes. Different types or quantities of carbon black provide different performance specifications for tires.
Generally speaking, tires are made up of approximately twenty or more different constituents or raw materials. Many different formulations of these raw materials are used. In fact, at least eighty different formulations are readily recognized in the industry for use in tire manufacturing. Different formulations are used for different parts of the tire. More particularly, different formulations are used for the tread portion, sidewall portion, and other portions of the tire. All of the formulations are vulcanized or fused during the tire manufacturing process to form the tire. Each formulation provides different performance characteristics for the tire. Such formulations are also used to make retreads for tires. Retreads represent only the tread portion of the tire and are vulcanized onto a used and/or existing tire to provide a tire with new tread. Silica and/or other raw materials are also used in tire/retread manufacture as a filler and/or as a networking agent. When silica is used in tire manufacture for networking purposes, a coupling agent is also used.
As a person skilled in the art readily understands, tire manufacturing involves adding polymer, networking agents, plasticisers, process oils, resins and/or fillers in a mixer, such as a Banbury mixer, and then the various components are vulcanized or fused to provide a homogeneous blended material which is used in a known manner, such as in a molding operation, to produce tires and retreads.
It is known in the tire industry that the compounds used in the tire formulation have an effect on the viscoelastic properties of the resulting tire. For example, plasticizers and process oils, like polymers, can have various glass transition temperatures (Tg) depending on the chemical structures. Paraffinic process oils and plasticisers such as dioctyl phthalate (DOP) have very regular structures and hence have low Tg's. Aromatic oils have large ring structures that hinder rotational motion and have high Tg's. The amount of change in the overall compound Tg is dependent on the oil's volume and Tg and can be determined in accordance with known formulas. The addition of oils also broadens the compound Tg range. In addition, the addition of oils or plasticizers have a softening effect on the compound and reduce the E'(G') elastic modulus and the E*(G*) complex modulus.
Resins also effect the viscoelastic properties of tires when used in tire formulations. For example, Phenolic tackifying resins and most hydrocarbon resins have higher Tg's than the compound polymer system and tend to raise the overall Tg and the tan delta of the compound. The above resins have a softening effect and reduce the E'(G') elastic modulus and the E*(G*) complex modulus. Crosslinked phenolic reinforcing resins and high styrene resins increase the E'(G') elastic modulus and the E*(G*) complex modulus. At higher temperatures (90+.degree. C.), the high styrene resins will go through the Tg have a softening effect on the compound. The phenolic reinforcing resins are permanently crosslinked with a methylene donor such as HMT or HMMM and do not soften at higher temperatures. A very low hysteresis, high hardness compound, can be created with a crosslinked phenolic reinforcing resin and very low levels of carbon black and silica.
Hysteresis in the bulk of a rubber product is defined as the energy lost when the rubber product is deformed and then released. Hysteresis is the result of internal friction and is evident as heat. Hysteresis is commonly measured as a temperature increase in a flexed specimen (heat build-up). It is widely known that when carbon black is added to a gum rubber, the rubber is generally reinforced, exhibiting increases in such properties as tensile strength, abrasion resistance, tear strength, modulus, etc. It is also widely known that carbon black increases the hysteresis of a rubber product.
While known formulations for tires and retreads have provided high quality products for many years, there is certainly room for improvement in such formulations and the resulting tire/retread products. Thus, a need exists for new and/or improved formulations and/or raw materials which are used in the manufacture of tires/retreads.